1. Field of the Invention
The present invention relates to a parameter identifier used to identify the mechanical time constant (that is, the moment of inertia) of a motor or the like.
2. Description of Related Art
The following conventional techniques are known in the art of parameter identification.
(1) A method for designing an adaptive observer taking account of external disturbance by extending state equations of a plant. This method is taught by Z. Iwai, "Problems in Adaptive Observers", SYSTEM AND CONTROL, Vol. 28, No. 6, pp. 354-363, 1984, Japanese Association of Automatic Control Engineers. PA1 x(t)=Ax(t)+bu(t)+fw(t), x(0)=x.sub.0 PA1 y(t)=c.sup.T x(t) PA1 w(t)=Dw(t), w(0)=w.sub.0 PA1 w(t)=d.sup.T w(t) PA1 x(t)=Ax(t)+bu(t) PA1 y(t)=c.sup.T x(t) PA1 e(t)=g(t).sup.T .zeta.(t)+f.sub.3 (t) PA1 g(t).sup.T =[z.sub.1 (t)T.LAMBDA., Z.sub.2 (t)T.LAMBDA.] PA1 .zeta.(t).sup.T =[(a-a(t)).sup.T, (b-b(t)).sup.T ] PA1 f.sub.3 (t)=c.sup.T e.sup.Kt x(0) PA1 (2) A parameter identification method disclosed in Japanese Patent Application Laying-Open No. 228285/1990 applied by the present assignee. In identifying the mechanical time constant of a motor, this application assumes that the load disturbance torque is constant or changes stepwise, and identifies the mechanical time constant on the basis of changes in the speed and changes in the driving torque. PA1 a model estimating the state variables and an output of the plant on the basis of identified parameters, and the input and output of the plant; PA1 a subtracter calculating an error by subtracting the output of the plant from the estimated output of the plant produced from the model; PA1 a delay circuit delaying the state variables produced from the model by N samples, where N is an integer which is not less than 1 or more than (n+m+1); and PA1 a parameter adaptive mechanism for adjusting the parameters on the basis of the delayed state variables and the error. PA1 a first delay circuit including serially connected (n+m) delay elements, each of which delays the output of the plant by one sample; PA1 first weighting means for obtaining (n+m) weighted linear combinations of the outputs of the delay elements of the first delay circuit, the first weighting means outputting the (n+m) weighted linear combinations as first state variables; PA1 first linear combination means for obtaining a linear combination of the first (n+m) state variables using the parameters identified as coefficients of that linear combination; PA1 a second delay circuit including serially connected (n+m) delay elements, each of which delays the input of the plant by one sample; PA1 second weighting means for obtaining (n+m) weighted linear combinations of the outputs of the delay elements of the second delay circuit, the second weighting means outputting the (n+m) weighted linear combinations as second state variables; PA1 second linear combination means for obtaining a linear combination of the second (n+m) state variables using the parameters identified as coefficients of that linear combination; and PA1 a subtracter producing a difference between the output of the first linear combination means and the output of the second linear combination means. PA1 a motor which is subject to a load disturbance; PA1 a parameter identifier identifying one or more parameters of the motor including n state variables, the motor being subject to a known disturbance represented by an m-order impulse train; and PA1 a regulator producing a torque command from a speed command, the regulator modifying the torque command in accordance with the identified parameters, PA1 the parameter identifier including:
This method supposes a plant expressed by the following equations corresponding to equations (5.1a) and (5.1b) of the above-mentioned reference.
In addition, a disturbance is given by the following equations corresponding to equations (5.2a) and (5.2b) of the reference.
From these equations, an (n+k) order extended system expressed by the following equations corresponding to equations (5.3a) and (5.3b) of the reference is obtained.
where n is the order of the plant and k is the order of the disturbance.
The method is arranged into a Kreisselmeier type adaptive observer by using a state variable filter expressed by the following equation corresponding to equation (5.8) of the reference. EQU z.sub.i (t)=K.sup.T z.sub.i (t)+cu.sub.i-1, z.sub.i (0)=0, i=1,2(u.sub.0 =y, u.sub.1 =u)
In addition, an error equation is given by the following equation corresponding to equation (5.9).
FIG. 1 shows a functional block diagram of the second conventional system. In this system, a parameter identifier 503 identifies the mechanical time constant on the basis of the changes in the speed .omega.(t), that is, the output y(t) of a motor 502, and the changes in the driving torque .tau.a(t), that is, the input u(t) of the motor 502. Accordingly, if the load disturbance d (t) added to the motor 502 is constant, the state equation in the discrete time system is given by equation (1). In equation (1), d(p)=d.sub.0 (constant), p designates a sampling interval, and T.sub.M denotes the mechanical time constant. ##EQU1##
Although the first conventional technique can identify the parameter (the mechanical time constant) correctly if the disturbance occurs at time 0, the identification error will increase if the disturbance randomly occurs because the.sup. parameter is reidentified by the disturbance. The identification error will further increase when the plant undergoes the feedback control by an adaptive mechanism, because the feedback component including the effect of the disturbance is applied to the input of the plant. This presents a problem in that it hinders correct identification.
Although the second conventional system operates correctly when the load torque is constant, because the effect of the load torque is eliminated in that case, the identification error occurs for a stepwise load disturbance because the changes in the speed and driving torque appear in the same sampling interval owing to the effect of an automatic speed regulator.
Generally speaking, the actual load disturbance changes slower than the control signal, and is randomly and repeatedly takes place during the operation. As a result, the identification error is liable to increase. In addition, since the second method is for a single-inertia mechanical system, it cannot be applied to a multiple-inertia mechanical system.